BenQ XL2420T allowed resolutions

I'm play Counter-Strike:Global Offensive competitively and would like some help.
Currently I'm playing the game on a BenQ XL2420T with a resolution of 1024 x 768 running at 120Hz. I'd really like to play on 1280 x 960 at 120Hz however, I occasionally get a "Out of Range" message and my monitor goes black. From my understanding, this means that my monitor cannot support that resolution. Recently, I emailed BenQ about this problem and the engineer tells me the same. However, when I go into my ATI video settings, it shows me that a desktop resolution of 1280 x 960 at 120Hz is a viable resolution (no italics on 120Hz to indicate it is not recommended). As such, I am quite puzzled as to why this resolution does not work, could someone give me some ideas about why this is so?

I'm currently using an ATI 7800 series card and a dual-link DVI cable to connect to the monitor. Also, I'm trying to run the game at 1280 x 960 @ 120Hz. Currently 1920 x 1080 @ 120Hz is fine as it's my native resolution.

Hmmm, a quick Google suggests that many people are having the same sort of problem. It may well be that BenQ is right, and the monitor simply cannot support that resolution. You could try using a different cable (Display Port if your particular card supports it), but apart for that, I can't think of anything to suggest apart from updating your GPU drivers if you have not done so already.

We'll wait and see if anybody else has a solution, but you might have to just use 1024x768, or sacrifice some FPS and up the resolution.